Usually the interior of an oral cavity is constantly supplied with saliva. The saliva contains such a protein as albumin and such an inorganic component as salt and fulfills many functions which are important for maintaining an optimum oral cavity environment such as keeping wet the interior of the oral cavity, pH buffering action, antibacterial effect and intraoral cavity washing effect.
However, it is said that the amount of secreted saliva decreases as one gets old, and in the case of an aged person, the drying within the oral cavity caused by a decrease in the amount of secreted saliva poses a problem. Further, irrespective of age, there sometimes is a case where the amount of secreted saliva decreases markedly by the influence of various diseases and medicines used for treatment of the diseases or by stress or the like against complicated social life conditions, with consequent drying of the interior of the oral cavity.
Particularly, the drying within the oral cavity during use of a denture is a recent problem. There are many denture users who feel a heavy stress against a life with a denture inserted into the oral cavity, in various scenes of daily life. It is known that the secretion of saliva decreases to an extreme degree by such a stress.
When using a denture, there sometimes is a case where a paste- or sheet-like denture base stabilizing adhesive is used to bond and fix the denture and the intraoral cavity tissue strongly with each other lest the denture should come off. However, bonding the denture, which is a foreign matter to a living body, forcibly into the oral cavity gives a heavy stress to the user of the denture in both body and mind. Consequently, there arises the problem that, simultaneously with the start of use of the denture, the secretion of saliva decreases markedly or is exhausted and the interior of the oral cavity becomes dry.
Such an oral cavity drying disease is generally called dry mouth and is known to give rise to intraoral cavity burning sensation, pain, glossodynia, dental caries, taste trouble, inflammation of the oral mucosa, erosion, formation of ulcer, formation of tongue plaque, bad breath, periodontal disease, difficulty of chewing, dysphagia (swallowing trouble), and difficulty of conversation. Moreover, there sometimes occurs a case where the denture is not fixed due to drying in the interior of the oral cavity and is rubbed against the periodontal tissue, thus inducing pain to the extent that it is impossible to eat a meal or make conversation. This is an extremely serious problem. In the case where the interior of the oral cavity is thus dried, even if the mouth is washed out, the dried condition in the oral cavity is not ameliorated although the interior of the oral cavity gets wet temporarily, thus giving rise to a very large number of serious pains in daily life. Such being the case, a keen demand exists for an appropriate measure against such intraoral cavity drying.
In view of such circumstances, such a composition as moderately stimulates the salivary gland to wet the interior of the oral cavity is now under development in order to prevent, ameliorate or relieve the intraoral cavity drying. In JP Hei 10 (1998)-182392A it is proposed to use a sialogogic agent such as an organic acid. However, since acidity is very stimulative and the taste differs depending on each individual person; besides, the durability of effect is deficient. For these reasons the use of such a sialogogic agent is limited. For example, in the case where the saliva secreting function is markedly deteriorated due to an operation for treatment of a disease or by radiotherapy, the above method of stimulating the salivary gland does not afford a satisfactory saliva secretion promoting effect and the drying in the oral cavity is not remedied.
Further, the development of artificial saliva and that of a gargling agent are under way for the purpose of remedying the drying in the oral cavity. Heretofore proposed are artificial saliva and a gargling agent with glycerin or hyaluronic acid incorporated therein (JP 2004-136102A and WO 00-056344). However, since those components are not originally present in large amounts with the saliva, there sometimes is a case where the feeling of use is not desirable for the user or there is not obtained a satisfactory effect. In JP Hei 9 (1997)-508898A there is developed artificial saliva containing a salivary protein such as mucin or albumin. However, there sometimes is used a protein derived from a mammal such as pig, thus giving rise to the problem of safety against humans. Such artificial saliva and gargling agent have so far encountered problems in point of durability of effect, taste and feeling of use.
On the other hand, in WO 00-05049 there is proposed a method wherein a material having biocompatibility is contained in the interior of a denture to enhance the hydrophilicity of a biocontact surface of the denture, thereby making the denture more compatible with the interior of the oral cavity. According to this method, however, a heavy burden may be imposed on the user because it is necessary to remake the denture. Therefore, there has been a demand for a simpler method wherein the surface of an existing denture is modified so as to become more compatible with the interior of the oral cavity.
Such being the case, there still exists a demand for a remedial measure for preventing, ameliorating or relieving such a problem as intraoral cavity drying during use of a denture and improving the stability of the denture during use.